Fly fishing reels require a spool that rotates freely whilst the fishing line is wound onto the spool, and that provides a braking means whilst the fishing line is withdrawing from the spool. As there are, of course, left and right handed anglers, this feature has to be reversible.
Traditionally, this mechanism has been achieved in a number of ways, but principally by utilising a series of springs with pawls engaging a gear on the back of the spool, or by using a sprag clutch or freewheel. However, using these traditional methods, it is necessary to dismantle the braking mechanism, remove and then change over either pawls or freewheels, in order to accommodate either the left or right handed angler.